Only duplicated an object, but on attempt to change its own texture, it simultaneously affects the texture of the object I sourced it from
When you duplicate an object you are not creating a new material.
Both objects share the same one.

You need to assing a new material to the copied objcect.

To the right of the material's name you will see a number, it indicates how many ojbects are sharing a material (in this case 2). If you click on the number you will create a copy of the material and assign it to the object.

Changing the material now will result in no changes on other objects.